Flash Memory Data Erasing Method Using Incremental Voltage Control
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Solution Overview
Problem
Conventional data erasing methods in flash memory cause uncontrolled drift in threshold voltage distribution due to large voltage pulses, leading to inefficient and potentially incomplete data erasure.
Innovation Solution
A method involving incremental stepping pulses for data erasing, followed by reading operations to determine the need for further erasure and recording voltages, culminating in a final erasing voltage calculated as the sum of an erasing verification voltage, final reading voltage, and recorded erasing voltage to control the threshold voltage distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If voltage pulses with large voltage level are used to erase memory cells, then the erasing speed is improved, but the threshold voltage distribution becomes uncontrolled and drifts too fast
Solution Approach 1:
The patent divides the erasing process into multiple incremental steps with progressively increasing voltage levels. Instead of applying a single large voltage pulse, the method applies several smaller voltage pulses in sequence (e.g., first pulse at voltage V1, second pulse at voltage V2>V1, and so on), allowing the threshold voltage distribution to be controlled and adjusted at each step while still achieving complete erasure.
Solution Approach 2:
The patent dynamically adjusts the voltage level applied to memory cells during the erasing process. The voltage level is not fixed but is progressively increased based on the state of the memory cells and the desired threshold voltage distribution. This dynamic adjustment allows the system to optimize between erasing speed and threshold voltage control throughout the erasing operation.
2Manufacturing precision
If incremental stepping pulse erase is used to control threshold voltage distribution, then the control precision is improved, but the erasing time increases due to multiple operations
Solution Approach 1:
The patent performs preliminary actions by applying incremental voltage pulses that progressively prepare the memory cells for complete erasure. Each preliminary pulse at a lower voltage level begins shifting the threshold voltage distribution in the desired direction, so that the final high-voltage pulse can complete the erasure more efficiently. This preliminary action reduces the total time required compared to applying the full erasure voltage from scratch.
Solution Approach 2:
The patent maintains continuous useful action during the erasing process by applying a sequence of voltage pulses without idle periods. Each pulse continues the erasing action from where the previous pulse left off, with the threshold voltage distribution continuously shifting toward the target erased state. This continuous action minimizes total erasing time while maintaining precise control over the threshold voltage distribution throughout the process.
Data Source
AI summary
A flash memory apparatus and data erasing method thereof. The data erasing method includes: setting a plurality of incremental erasing voltages sequentially, and operating a plurality of data erasing operations on memory cells according to the erasing voltages; recording a recoded erasing voltage corresponding to the last data erasing operation; setting a plurality of incremental reading voltage sequentially, operating a plurality of data reading operations on the memory cells, and recording a final reading voltage corresponding to the last reading operation; setting a final erasing voltage for operating a final erasing operation on the memory cells, wherein a voltage level of the final erasing voltage equals to a sum of voltage levels of an erasing verification voltage, the final reading voltage and the recorded erasing voltage.